The present invention relates generally to the components of laser systems and specifically to the design of an electron beam gun foil support.
It is well known in the art that lasers of various types are in use and experimentation of new types are under study. Such lasers include solid state, chemical and gaseous types.
The laser utilizes the interaction of electromagnetic radiation with a material having an appropriate set of discrete energy levels.
For example, gaseous laser media with electron beams discharged across the gas are old in the art. There are many categories of gaseous laser media such as the molecular media exemplified by CO.sub.2. Of recent interest have been the rare gas excimer lasers, and the rare gas halide excimer lasers, and the rare gas atomic oxygen and the rare gas atomic iodine transfer lasers. For example, laser action was reported for an electron-beam pumped apparatus for bands of KrF and XcCl in Applied Physics Letters 27, 350 (1975). The excimer systems are well known for their efficiency derived in part from a bound excited state and weakly bound or unbound lower state, the excited state having a lifetime of typically 10 nanoseconds. Interest in the above lasers is due additionally to their ultraviolet and visible wavelengths. Such lasers are useful in laser isotope separation at relatively low energy per pulse (greater than or equal to one joule) and at high repetition rates (greater than or equal to 1 kHz). These lasers are also useful in attaining laser fusion which requires much higher energy pulses but much lower repetition rates. Such lasers are useful for other purposes known to persons working in the laser art.
Among the major components of a gaseous type laser system is an electron beam source, having a discharge cell separated from a vacuum by a foil, such as the gas discharge laser systems described in U.S. Pat. No. 4,143,336 issued to Searles et al on Mar. 6, 1979 and U.S. Pat. No. 4,230,994 issued to Bradley on Oct. 28, 1980 and incorporated herein by reference.
In high power electron guns the heat load on the foil support can be very severe; as high as 750 watts/cm.sup.2 on the (conventional design) support itself. The support structure must also provide cooling for the foil. By comparison, the loss in the foil is typically as high as 75 watts/cm.sup.2. So consequently, the cooling burden is nearly all from the foil support. A method is needed which reduces this burden by a factor of three or more which results in a much simpler cooling system and a far more reliable foil due to the fact it can now be simpler cooling system and a far more reliable foil due to the fact it can now be more easily cooled. Another advantage would be the fact that the electron transmission efficiency would be increased by about a factor of up to two. This means that the current emission density on the cathode is reduced correspondingly and the cathode life reliability and performance all improve. Also, the overall system efficiency is improved. For example, a large excimer laser electron gun may require 100 megawatts average power with a conventional foil support.
In view of the foregoing discussion, it is apparent that there exists the need for an improved high efficiency electron beam gun foil support that reduces the power loss and improves the electron transmission efficiency. The present invention is directed towards satisfying that need.